Another screenshot, this time from Episode 1 of the Dirk Gently TV series1. There are several pencils in this episode. One of them is easy to identify and plays an important role: it’s being used for shading paper to reveal a message.

The TV series seems to be loosely based on the book, with different episodes picking up different plots from Douglas Adams’ book (at least that’s the impression I have so far, after watching the pilot and episode 1. Future episodes might be different).